The present invention relates to a process for treating a fibrous structure containing polyester. It has been broadly known that the treatment of polyester fibrous structures with alkali develops a soft "hand" by partial dissolution and removal of certain materials. This treatment is primarily important for processing polyester fibrous structures.
Furthermore, it has been also known that mixtures of fibers that are easily soluble in alkalis and fibers that are difficult to dissolve in alkalis, when treated with alkalis, can produce a product having an excellent soft hand by dissolution and removal of the easily soluble fibers. However, this treatment requires a considerably long time to complete, and also results in some extent of damage by the alkali. This leads to unexpected deterioration of physical properties of the product.
On the other hand, when a more soluble component is used as the easily soluble fibers, the fibers are inadequate when subjected to mixing, blending, knitting and weaving processes, due to deterioration of physical properties. They also suffer from difficulty of fiber spinning (extruding).
The alkali treatment of mixtures of fibers, therefore, is not used in practice at present, although an outstandingly soft hand can be obtained.
When conjugated (composite) fibers contain an easily alkali-soluble component and a difficultly alkali-soluble component, and are treated with alkali to obtain micro (super) fine or special shape fibers, the problem is even more serious, since fine fibers which must remain in the structure are simply dissolved and thereby removed from the structure.
As a result of intensive studies, we have found a process for selectively dissolving only the easily alkali-soluble polyester components but not the difficultly alkali-soluble components--all in a short time and with convenience and efficiency.